Victoria Azarenka consulted a set of revision notes to help her edge out Germany’s Angelique Kerber and reach the US Open last 16.
Azarenka defeated the number 11 seed 7-5 2-6 6-4 after an enthralling match in Arthur Ashe Stadium, which lasted two hours and 52 minutes.
Kerber saved five match points in the final set to spark hopes of a comeback but Azarenka held her nerve to book a fourth-round meeting with American Varvara Lepchenko.
Lepchenko beat another German, Mona Barthel, in three sets.
Azarenka is fast-establishing herself as a major challenger at Flushing Meadows and the number 20 seed furthered her reputation with another powerful display.
The Belarusian drew inspiration, however, from an unusual source as she was seen regularly studying notes from her racquet bag at changes of ends.
“I started doing it not too long ago,” Azarenka said.
“It’s just something that I feel will keep me a little bit entertained during changeovers.
“Sometimes it gets a little quiet so I just want to make sure I’m focused on what I have to do.
“I write different things for myself, sometimes something to make sure I stay focused.
“I wrote this thing which was hilarious to me yesterday. It was so stupid, but it made me laugh so hard.
“I just wrote it to keep me relaxed sometimes.”
Lepchenko is ranked 46th in the world, 20 spots below Azarenka, and has never reached the fourth round in New York before.
The 29-year-old said she would have nothing to lose against her next opponent but Azarenka poured cold water on that approach.
“Everybody has something to lose,” Azarenka said.
“You have (ranking) points to lose. You have money to lose. You have opportunity to lose.
“I guess it’s a way to take the pressure off yourself. And for me, I love pressure. It makes me better.
“I don’t wish to have pressure, but it’s something that, I don’t know, I think I love to rise to the occasion. It’s challenging and motivating for me.”
Fifth seed Petra Kvitova progressed to the last 16 after she thrashed Anna Karolina Schmiedlova and the Czech will now face Britain’s Johanna Konta, who knocked out 18th seed Andrea Petkovic.
Australia’s 2011 champion Samantha Stosur and Italian Flavia Pennetta are also safely through.
Stosur beat Sara Errani in three sets while Pennetta also triumphed in a decider against Petra Cetkovska.
Germany’s Sabine Lisicki had to come from a set down to overcome Czech Barbora Strycova and she now faces second seed Simona Halep, who defeated American Shelby Rogers.